Universal coverage of a second generation (2G) or third generation (3G) network such as global system for mobile communications (GSM) or wideband code division multiple access (WCDMA) has basically been implemented.
With the development of Long Term Evolution (LTE) network technologies, the LTE network has covered some urban areas and traffic hotspot areas, and in this way, in current communications networks, the LTE network coexists with the 2G or 3G network.
In a calling process, user equipment (UE) may enter the 2G or 3G network from the LTE network, and because bearing mechanisms of the LTE network and the 2G or 3G network are different, the user equipment needs to hand over from a packet switching (PS) domain to a circuit switching (CS) domain, and an interruption of a voice call may occur, thereby affecting continuity of a voice call of a user.
Circuit switched fallback (CSFB) is: when user equipment (UE) in coverage of LTE processes a voice service, the UE first returns to a network having a CS domain, and processes the voice service in the network having a CS domain, thereby achieving an objective of providing a conventional voice service for a user in an LTE network by re-using an existing CS domain device. In the prior art, the UE needs to hand over from the LTE network to a PS domain of the 2G or 3G network, or be redirected from the LTE network to the 2G or 3G network, and then initiates a CS domain connection in the 2G or 3G network.
In the prior art, even when the UE can support a handover from the LTE network to the CS domain of the 2G or 3G network, the UE also needs to move to the PS domain of the 2G or 3G network before initiating a voice call, thereby causing that entire voice call duration is relatively long, and user experience is poor.